Ugh, nitrogen. If you pay $0.01 for nitrogen in your tires, that's WAY too much. I wish nitrogen would just go away.

Some additional rules of thumb:
1) Tires increase/decrease about 1PSI per 10 degrees of ambient temperature. (Nitrogen or not)
2) For a lot of highway driving, I will inflate tires to about 4PSI over the sticker pressure. Much more than that, and people will start to notice a harsher ride. Doing so will yield about 0.2-0.3 MPG improvement. I run mine at 5PSI over sticker.
3) For low-speed local driving (i.e. mom driving her kids to school) I set to the factory recommended pressure because too many other factors influence MPG for that type of driving, and they don't need the harshness.
4) The higher the tire pressure, the less likely you are to damage a sidewall if you hit a pothole. This is another reason you need to check your PSI in the winter - colder weather (i.e. lower PSI) PLUS more potholes...
5) When you get rid of your old tires, look at how they are worn, If the centers of the tread are worn then your tire pressure was too high. If your edges were worn, your pressure was too low.
6) Higher weight = higher PSI. For example, extra weight in the front (engine) means you need a higher PSI. If you tow or put a lot of luggage in the trunk (or have heavy passengers in the back seat) then bump up the PSI on the rear tires a bit.
7) Don't get too excited about changing your PSI at the drag strip, unless you run a drag tire. The lower PSI on drag tires allows the sidewalls to flex, but doesn't have nearly the same benefit on a street tire.
8) PSI tends to climb about 3 PSI when highway driving due to temperature increase (2-4 PSI depending on a bunch of factors).
9) I rotate my tires about 2-3 times over the life of the tires, and keep an eye on treadwear. You don't need to rotate/balance every oil change.
10) Put your best tires in the rear, especially in winter. That gives you stability in a panic stop- if your car stays straight, at least you can still steer... if your rear end swings around because the tires suck, then your steering wheel becomes pretty useless too. Oh yeah, change your rear shocks/struts at about 75k miles too, they are more important than the fronts.

-BC